This invention relates to the field of ship cargo hatch covers, and mechanisms for opening and closing such covers.
It is impossible to exaggerate the importance of cargo hatch covers to the safety, watertight integrity and operability of a ship. Crew safety and ship survival may depend on how well hatch covers operate.
Hatch Cover actuation mechanisms fall into the category of cargo access equipment. Such actuators are shown in, for example:
U.S. Pat. No. 3,211,122 to Barlow discloses a power operated hatch cover mechanism in which a spaced pair of rotary hydraulic actuators pivot cargo hatch panels through gears.
U.S. Pat. No. 3,104,643 to Vallet discloses a hydraulic cylinder system for opening or locking a closed hatch cover. The hydraulic cylinder is suspended between two pivot points under one of two opposed hatch covers.
U.S. Pat. No. 3,077,225 to Aarvold, in disclosing a design for the hinges of a cargo hatch cover, shows the use of a hydraulic motor for opening and closing the hatch cover.
U.S. Pat. No. 3,050,026 to Ligh shows an opening system involving two coordinated hydraulic actuators.
U.S. Pat. No. 2,891,500 to Appleton shows a combined hydraulic and cable system to open the hatch covers. This system results in extensive cable runs across the cargo deck.
U.S. Pat. No. 2,737,919 to McRae discloses a system having a multiplicity of relatively narrow hatch covers which individually can be rotated to a vertical or horizontal position and, in a vertical position, may be moved along the hatch by motors and gears.
German patent 1,506,251 discloses a hydraulic hatch cover with self contained hydraulics beneath the hatch cover.
Swedish patent 221194 discloses a mechanical, gear driven on track hatch cover actuator which appears to be a variant on a "single pull MacGregor" system, a cable pull system in which a cable is reeved through all the wheels supporting all the hatch cover panels, and used to pull the covers to a removed position.
Belgian patent 644496 appears to discloses a cargo hatch cover actuation mechanism comprising a belt driven gear, affixed to hinges to fold adjacent covers about said hinges.
Japanese patent 199789 appears to disclose a hydraulically actuated cargo hatch cover mechanism
Australian patent 241030 discloses a hydraulic hatch cover actuating mechanism, with hinging to maximize closing force near the cover closed position.
Danish patent 97330 discloses an actuating mechanism in which a freely pivoted hydraulic cylinder bears on a link, which is pivotally attached to two interlocked gears, each fixed to a hatch cover section, causing the gear to pivot around each other as a hinge.
The principal objection to the use of exposed hydraulic is the possible contamination of bulk cargos, especially grains, from hydraulic fluid leakage. Since hydraulic systems are uncommon aboard ship, few ships have on board maintenance capabilities for such systems, and such leaks and failures become increasingly common as ship systems age.
An equally serious objection is the consequences of system failure; loss of hydraulic pressure can result in a sudden fall of the hatch covers. Since a hatch cover is a large, heavy metal object, damage by a falling hatch cover can be severe, and may result in structural damage to the ship hull if the cover falls into the hold. Cable driven systems likewise can collapse if the cable snaps. Such failure additionally can result in cable whiplash, which endangers all crew.